1. Field of the Invention
The present invention relates to telephone test sets having an auxiliary amplifier and speaker for permitting listening to signals on a telephone line during repair procedures.
2. Description of the Prior Art
The assignee of the present invention sold an amplifier specifically designed for connection to the Model TS-21 test set. This amplifier was contained in a separate case which had a plug-in connector for connection to the Model TS-21 test set to amplify and generate an audio signal in a loudspeaker of the signals present on a telephone line being tested by a technician using the test set. The amplifier was shunted across the receiver within the telephone test set. It contained an on/off switch and a volume control. The amplifier contained an electronic sensor which activated the amplifier in response to the detection of loop current. The system would not work on "dry loops" which were not connected to the battery of the central office.
The prior art system did not permit amplification of line signals in the so-called "monitor model". In the monitor mode, prior art telephone test sets capacitively couples signals on the line to make them audible over the receiver in the telephone test set without drawing sufficient loop current to disturb any conversations which were ongoing on the line. Finally, the prior art amplifier in combination with the Model TS-21 test set did not permit automatic muting of the transmitter and receiver when the amplifier was activated.